A fresh-keeping bag for food storage and a preparation method thereof

Abstract

The application provides a fresh-keeping bag for food storage and a preparation method thereof, and belongs to the technical field of food preservation, and comprises a three-layer composite film bag body, a cellulose nanocrystal array is arranged at the bottom of the inner wall of the inner layer of the three-layer composite film bag body, and a pH indicating window is arranged on the outer wall of the three-layer composite film bag body; the pH indicating window changes color when the pH exceeds a threshold range; the pH indicating window arranged on the outer wall of the fresh-keeping bag directly warns food spoilage, a moisture management system composed of a cellulose nanocrystal array, hydrophilic water guide fibers and a polydopamine photothermal layer is arranged inside, the moisture management system prolongs the fresh-keeping period, and a cross-shaped reinforcing rib and a hemp fiber reinforced net are arranged at the bottom of the fresh-keeping bag, so that the damage rate under load is reduced, and the durability is improved.

Description

Technical Field

[0001] This invention belongs to the field of food preservation technology, specifically a food preservation bag for food storage and its preparation method. Background Technology

[0002] With rising living standards and heightened health awareness, consumers have increasingly stringent demands for food preservation. As a crucial tool for daily food storage, food preservation bags directly impact the shelf life and safety of food. Currently, most food preservation bags on the market are made from traditional petroleum-based plastics such as polyethylene (PE) and polypropylene (PP). While these materials possess good flexibility and sealing properties, they are difficult to degrade in the natural environment, and their widespread use easily causes "white pollution," contradicting the globally advocated low-carbon and environmentally friendly principles. Research has found that polyethylene (PE) materials can be modified to combine with zinc ions to enhance preservation. Zinc ions, as a safe and highly effective antibacterial component, can disrupt the cell membrane structure of microorganisms, inhibiting their reproduction and thus slowing down the spoilage process. Some PE-based food preservation bag products have already attempted to improve antibacterial properties by adding zinc ion compounds, extending the shelf life of meat, fruits, and vegetables to some extent.

[0003] Meanwhile, existing food storage bags have a relatively limited function, mainly relying on physical barriers to delay food spoilage. They are insufficient to address issues such as moisture accumulation and microbial growth that occur during the storage of different foods (such as fruits, vegetables, meats, and cooked foods). For example, moisture released by the respiration of fruits and vegetables easily condenses inside the bag, leading to increased local humidity and accelerating mold growth. Acidic substances produced during the spoilage of high-protein foods such as meat cannot be effectively absorbed or converted, and the spoilage process is difficult to monitor visually, easily posing food safety risks.

[0004] Furthermore, some modified food storage bags attempt to improve preservation by adding antibacterial agents, but these methods suffer from uneven dispersion of antibacterial components and poor long-lasting performance. Moreover, most products do not consider the biocompatibility and environmental friendliness of the materials. In terms of structural design, traditional food storage bags are mostly single-layer film structures, lacking targeted moisture management and gas regulation modules, making it difficult to meet the needs of refined storage.

[0005] In view of the above problems, this invention proposes a food storage bag and its preparation method. Based on composite film technology of biodegradable materials such as polylactic acid (PLA) and polybutylene terephthalate (PBAT), combined with antibacterial modification, structural optimization and sensor design, the food storage bag achieves synergistic improvement in environmental protection, functionality and safety, and provides a more reliable solution for food storage. Summary of the Invention

[0006] The purpose of this invention is to address the aforementioned problems in existing technologies by proposing a food preservation bag for food storage and its preparation method.

[0007] The objective of this invention can be achieved through the following technical solutions:

[0008] A food storage bag, comprising:

[0009] Three-layer composite film bag;

[0010] The inner layer of the three-layer composite film bag comprises the following raw materials in parts by weight: 60-80 parts of polylactic acid, 20-40 parts of polybutylene adipate terephthalate, 1-3 parts of modified hemp fiber, 0.5-2 parts of composite antibacterial agent, and 0.3-0.8 parts of ADR chain extender;

[0011] The outer layer of the three-layer composite film bag comprises the following raw materials in parts by weight: 70-90 parts of polylactic acid and 10-30 parts of polybutylene terephthalate.

[0012] The intermediate support layer of the three-layer composite membrane bag comprises the following raw materials in parts by weight: 60-80 parts of high-density polyethylene, 10-20 parts of metallocene polyethylene, 5-10 parts of polyethylene grafted with maleic anhydride, 5-10 parts of TPE or SEBS, 3-8 parts of nano zinc oxide, and 0.5-1.5 parts of coupling agent.

[0013] The total thickness of the three-layer composite membrane bag is 50~70μm, and the thickness ratio of the inner layer, the middle support layer and the outer layer is 1:1.5~2.5:1.

[0014] The bottom of the inner wall of the inner layer of the three-layer composite membrane bag is provided with a cellulose nanocrystal array, the cellulose nanocrystal array covering an area of ​​20-40% of the total area of ​​the bottom of the inner wall. The top inner wall of the bag is provided with a laser-engraved micro-conical groove water storage area. Hydrophilic water-conducting fibers connect the cellulose nanocrystal array and the water storage area. The surface of the water storage area is covered with a polydopamine photothermal layer with a thickness of 50-100nm.

[0015] The outer wall of the three-layer composite membrane bag is provided with a pH indicator window, which contains the following components by mass percentage: bromocresol purple 0.5~1.5%, silica fluorescent microspheres 2~4%, and hydroxyethyl cellulose gel 94.5~97.5%;

[0016] The pH indicator window changes color when the pH exceeds a threshold range.

[0017] Preferably, the modified hemp fiber is treated with silane coupling agent KH-550 and has a length of 50~200μm and a diameter of 10~30μm;

[0018] The composite antibacterial agent is a titanium dioxide and graphene oxide antibacterial agent, with a mass ratio of titanium dioxide to graphene oxide of 1:0.2~0.5.

[0019] Preferably, the cellulose nanocrystal array is located 0.5-2.0 cm above the heat-sealing line at the bottom of the bag, and is assembled from carboxymethylated cellulose nanocrystals with a diameter of 20-50 nm using a 0.5-2T magnetic field, with an array density of 102. 6 ~10 7 root / mm 2 ;

[0020] The hydrophilic and water-conducting fiber is a long carboxymethylated cellulose fiber with a diameter of 20~50μm.

[0021] Preferably, the depth of the micro-conical groove water storage area is 100~300μm;

[0022] The visible light absorption rate of the polydopamine photothermal layer is ≥90%.

[0023] Preferably, the dimensions of the bag are 25-35cm in length, 18-25cm in width, and 10-25cm in height;

[0024] Among them, the bottom of the bag is heat-sealed to form a cross-shaped reinforcing rib, with a rib width of 3~5mm and a thickness of 150~200μm;

[0025] The bottom of the inner layer of the bag is embedded with hemp fiber reinforcement mesh with a density of 20-30 fibers / cm².

[0026] A method for preparing a food storage bag includes the following steps:

[0027] S1. Material preparation and pretreatment:

[0028] S1a. Preparation of inner layer materials: Weigh polylactic acid, polybutylene adipate terephthalate, modified hemp fiber, titanium dioxide and graphene oxide composite antibacterial agent, and ADR chain extender according to the weight parts, place them in a high-speed mixer and mix at 60-70℃ for 5-10 minutes, and discharge for later use;

[0029] S1b. Preparation of outer layer material: Weigh polylactic acid and PBAT according to the weight parts, place them in a high-speed mixer and mix at 55-65℃ for 5-8 minutes, then discharge for later use;

[0030] S1c. Preparation of intermediate layer material: Weigh high-density polyethylene and metallocene polyethylene according to the weight parts, add nano zinc oxide and coupling agent, mix at 80-90℃ for 8-12 minutes to fully surface treat the nano zinc oxide; then add polyethylene grafted with maleic anhydride and TPE, continue mixing at 75-85℃ for 5-8 minutes, and discharge for later use.

[0031] S2, Three-layer co-extrusion blown film: Three single-screw extruders are used to separately feed the inner layer, outer layer, and middle layer materials, wherein:

[0032] The inner extruder temperature is set to 160-180℃;

[0033] The temperature of the intermediate layer extruder is set to 180-200℃;

[0034] The outer extruder temperature is set to 150-170℃;

[0035] The three-layer melt is composite blow-molded through a co-extrusion die, with the blow-up ratio controlled at 2.5-3.5 and the cooling air ring temperature at 10-15℃, to obtain a three-layer composite preform.

[0036] By adjusting the screw speed of the three-layer extruder, the thickness ratio of the inner layer, middle layer, and outer layer can be controlled to be 1:1.5-2.5:1, with a total film thickness of 50-70μm;

[0037] S3. Bag making and reinforcement: The three-layer composite film is cut into film sheets of predetermined size, with a length of 50-70cm and a width of 36-50cm, corresponding to the unfolded size of the finished bag. During the bag making process, the hemp fiber reinforcement mesh is first pre-laid on the bottom of the bag body corresponding to the position of the inner layer film. It is then embedded into the inner layer under a pressure of 0.3-0.5MPa by a roller pressing device. Then, it is heat-sealed for 3-5 seconds at 160℃ and 0.5MPa pressure, which at the same time forms a bottom seal and a cross-shaped reinforcing rib. The rib width is 3-5mm and the thickness is 150-200μm.

[0038] S4. Functional Structure Processing:

[0039] S4a. Apply a 1-3wt% carboxymethylated cellulose nanocrystal dispersion to the bottom of the inner wall of the bag, 0.5-2.0cm above the heat-sealing line, and dry it at 40-50℃ in a 0.5-2T magnetic field for 30-60 minutes to form a vertically oriented cellulose nanocrystal array with an array density of 106-107 nanocrystals / mm², covering an area of ​​20-40% of the total area of ​​the bottom of the inner wall.

[0040] S4b. A micro-conical groove water storage area is processed on the inner wall area at the top of the bag using laser micro-engraving technology, with a groove depth of 100-300μm;

[0041] S4c. Carboxymethylated cellulose long fibers with a diameter of 20-50 μm are used as hydrophilic water-conducting fibers, with their two ends fixed in the cellulose nanocrystal array region and the water storage region groove, respectively.

[0042] S4d. Deposit a polydopamine photothermal layer on the surface of the groove in the water storage area, and immerse it in dopamine hydrochloride Tris-HCl buffer for 24-48 hours at pH=8.5 to form a photothermal layer with a thickness of 50-100nm.

[0043] S5. Preparation of the indicator window: Apply pH indicator window gel to a predetermined position on the outer wall of the bag. The gel composition by mass percentage is: 0.5-1.5% bromocresol purple, 2-4% silica fluorescent microspheres, and 94.5-97.5% hydroxyethyl cellulose gel. The coating thickness is 20-50 μm, and it is dried and cured at 40℃. The pH response threshold of the indicator window is 6.0-6.5±0.2.

[0044] S6. Post-processing and packaging: The finished bags are subjected to ultraviolet sterilization treatment, and the sealing performance, pH indicator window function and photothermal layer performance are tested. Qualified products are packaged and put into storage.

[0045] Preferably, in step S2, the melt flow rate ratio of the three-layer extruder is controlled to be inner layer: middle layer: outer layer = 1:1.8-2.2:1.

[0046] Compared with existing technologies, the food preservation bag and its preparation method have the following advantages:

[0047] 1. The present invention provides a food storage bag and its preparation method, which has comprehensive and efficient preservation function. The composite antibacterial agent in the inner layer can effectively inhibit the reproduction of microorganisms. The moisture management structure can handle the condensation in the bag in time through the cellulose nanocrystal array, hydrophilic water-conducting fiber, water storage area and polydopamine photothermal layer, thus extending the food shelf life.

[0048] 2. The present invention provides a food storage bag and its preparation method. The inner and outer layers are made of biodegradable materials such as polylactic acid (PLA) and polybutylene terephthalate adipate (PBAT), which significantly reduces the proportion of traditional petroleum-based plastics. At the same time, the middle layer effectively concentrates functional additives such as nano zinc oxide, which reduces the overall environmental impact while meeting the usage requirements.

[0049] 3. The present invention provides a food storage bag and its preparation method, which has intelligent monitoring and structural stability. The pH indicator window on the outer wall can intuitively reflect the food spoilage state. The cross-shaped reinforcing ribs and hemp fiber reinforcement mesh at the bottom enhance the load-bearing capacity and sealing performance of the bag, thereby improving its reliability.

[0050] In summary, this invention provides a food storage bag and its preparation method. By setting a pH indicator window on the outer wall of the food storage bag, it provides a visual warning of food spoilage. The internal moisture management system, consisting of a cellulose nanocrystal array, hydrophilic water-conducting fibers, and a polydopamine photothermal layer, extends the shelf life. The bottom of the food storage bag is equipped with cross-shaped reinforcing ribs and hemp fiber reinforcement mesh, which reduces the breakage rate under load and improves durability. Detailed Implementation

[0051] The following are specific embodiments of the present invention, which further describe the technical solution of the present invention, but the present invention is not limited to these embodiments.

[0052] A food storage bag, comprising:

[0053] Three-layer composite film bag;

[0054] The inner layer of the three-layer composite film bag comprises the following raw materials in parts by weight: 60-80 parts of polylactic acid, 20-40 parts of polybutylene adipate terephthalate, 1-3 parts of modified hemp fiber, 0.5-2 parts of composite antibacterial agent, and 0.3-0.8 parts of ADR chain extender;

[0055] The outer layer of the three-layer composite film bag comprises the following raw materials in parts by weight: 70-90 parts of polylactic acid and 10-30 parts of polybutylene terephthalate.

[0056] The intermediate support layer of the three-layer composite membrane bag comprises the following raw materials in parts by weight: 60-80 parts of high-density polyethylene (HDPE), 10-20 parts of metallocene polyethylene (mPE), 5-10 parts of polyethylene grafted maleic anhydride (PE-g-MAH), 5-10 parts of TPE or SEBS, 3-8 parts of nano zinc oxide, and 0.5-1.5 parts of coupling agent.

[0057] Among them, polylactic acid (PLA) bio-based biodegradable material is used to provide basic mechanical strength and gas barrier properties, and the degradation product lactic acid has weak antibacterial properties; polybutylene adipate terephthalate (PBAT) is used to compensate for the brittleness of PLA, improve flexibility and heat-sealing performance, and improve processability when blended with PLA; modified hemp fiber is used to enhance the chemical bonding between the fiber and the PLA / PBAT interface and reduce phase separation; micron-sized particles serve as a reinforcing phase to improve puncture resistance while retaining biodegradability; in the TiO2 / GO composite antibacterial agent, TiO2 (photocatalyst) generates reactive oxygen species (·OH) through ultraviolet light excitation, which destroys the microbial cell membrane; graphene oxide (GO) nanosheets physically cut the cell membrane and synergistically expand the antibacterial spectrum with TiO2; ADR chain extender reacts with the terminal carboxyl groups of PLA / PBAT through epoxy groups to improve melt strength and inhibit film breakage during blown film process.

[0058] HDPE and mPE are the matrix resins, together forming the mechanical framework of the intermediate layer; while PE-g-MAH is a compatibilizer, its main function being to improve the interfacial bonding between the intermediate layer (PE group) and the inner layer (PLA group). PLA molecules have -OH (hydroxyl) and -COOH (carboxyl) groups at their ends. At processing temperatures, the anhydride ring of maleic anhydride readily undergoes esterification or amidation reactions with these groups, forming strong covalent bonds.

[0059] The total thickness of the three-layer composite membrane bag is 50-70 μm, with the thickness ratio of the inner layer, intermediate support layer, and outer layer being 1:1.5-2.5:1. The thicker outer layer enhances mechanical protection, while the thinner inner layer retains the functional concentration of antibacterial agents or chain extenders, reducing costs. The nano-zinc oxide in the intermediate layer can slowly release Zn under certain humidity conditions. 2+ It acts on the inner surface through interfacial diffusion or vapor-phase migration, providing auxiliary antibacterial function. The core antibacterial mode avoids direct contact between the antibacterial agent and food, making it safer and providing long-term antibacterial effect.

[0060] The bottom of the inner wall of the inner layer of the three-layer composite membrane bag is provided with a cellulose nanocrystal array, the cellulose nanocrystal array covering an area of ​​20-40% of the total area of ​​the bottom of the inner wall. The top inner wall of the bag is provided with a laser-engraved micro-conical groove water storage area. Hydrophilic water-conducting fibers connect the cellulose nanocrystal array and the water storage area. The surface of the water storage area is covered with a polydopamine photothermal layer with a thickness of 50-100nm.

[0061] The vertical cellulose nanocrystal array is carboxymethylated to introduce -COOH, enhancing its hydrophilicity and adsorbing condensate through capillary action. Magnetic field orientation aligns the nanocrystals along the magnetic field direction, forming vertical channels that accelerate the directional migration of water molecules. Laser-engraved conical grooves expand the specific surface area, increasing water storage capacity. Carboxymethylated cellulose long fibers connect the bottom array to the water storage area, forming a tiered moisture-wicking system of "bottom water absorption - top water storage." The polydopamine layer has certain hygroscopic and photothermal conversion capabilities, assisting in water evaporation under light conditions and still adsorbing water through its porous structure in the absence of light.

[0062] The outer wall of the three-layer composite membrane bag is provided with a pH indicator window, which contains the following components by mass percentage: bromocresol purple 0.5~1.5%, silica fluorescent microspheres 2~4%, and hydroxyethyl cellulose gel 94.5~97.5%;

[0063] The pH indicator window changes color when the pH exceeds the threshold range, turning from yellow to purple when the pH is above the threshold (indicating meat spoilage), and from yellow to red when the pH is below the threshold (indicating fruit and vegetable spoilage); the silica fluorescent microspheres reflect the excitation light, enhancing the color contrast; the hydroxyethyl cellulose gel three-dimensional network fixes the indicator, controlling the ion permeation rate.

[0064] The modified hemp fiber is treated with silane coupling agent KH-550 and has a length of 50~200μm and a diameter of 10~30μm.

[0065] The composite antibacterial agent is a titanium dioxide and graphene oxide antibacterial agent, with a mass ratio of titanium dioxide to graphene oxide of 1:0.2~0.5.

[0066] The cellulose nanocrystal array is located 0.5-2.0 cm above the heat-sealing line at the bottom of the bag. It is composed of carboxymethylated cellulose nanocrystals with a diameter of 20-50 nm, oriented and assembled using a 0.5-2T magnetic field, with an array density of 102. 6 ~10 7 root / mm 2 ;

[0067] The hydrophilic and water-conducting fiber is a long carboxymethylated cellulose fiber with a diameter of 20~50μm.

[0068] The depth of the micro-conical groove water storage area is 100~300μm;

[0069] The visible light absorption rate of the polydopamine photothermal layer is ≥90%.

[0070] The dimensions of the bag are 25-35cm in length, 18-25cm in width, and 10-25cm in height;

[0071] Among them, the bottom of the bag is heat-sealed to form a cross-shaped reinforcing rib, with a rib width of 3~5mm and a thickness of 150~200μm;

[0072] The bottom of the inner layer of the bag is embedded with hemp fiber reinforcement mesh with a density of 20-30 fibers / cm².

[0073] A method for preparing a food storage bag, comprising:

[0074] S1. Material preparation and pretreatment:

[0075] S1a. Preparation of inner layer materials: Weigh polylactic acid, polybutylene adipate terephthalate, modified hemp fiber, titanium dioxide and graphene oxide composite antibacterial agent, and ADR chain extender according to the weight parts, place them in a high-speed mixer and mix at 60-70℃ for 5-10 minutes, and discharge for later use;

[0076] S1b. Preparation of outer layer material: Weigh polylactic acid and PBAT according to the weight parts, place them in a high-speed mixer and mix at 55-65℃ for 5-8 minutes, then discharge for later use;

[0077] S1c. Preparation of intermediate layer material: Weigh high-density polyethylene and metallocene polyethylene according to the weight parts, add nano zinc oxide and coupling agent, mix at 80-90℃ for 8-12 minutes to fully surface treat the nano zinc oxide; then add polyethylene grafted with maleic anhydride and TPE, continue mixing at 75-85℃ for 5-8 minutes, and discharge for later use.

[0078] S2, Three-layer co-extrusion blown film: Three single-screw extruders are used to separately feed the inner layer, outer layer, and middle layer materials, wherein:

[0079] The inner extruder temperature is set to 160-180℃;

[0080] The temperature of the intermediate layer extruder is set to 180-200℃;

[0081] The outer extruder temperature is set to 150-170℃;

[0082] The three-layer melt is composite blow-molded through a co-extrusion die, with the blow-up ratio controlled at 2.5-3.5 and the cooling air ring temperature at 10-15℃, to obtain a three-layer composite preform.

[0083] By adjusting the screw speed of the three-layer extruder, the thickness ratio of the inner layer, middle layer, and outer layer can be controlled to be 1:1.5-2.5:1, with a total film thickness of 50-70μm;

[0084] S3. Bag making and reinforcement: The three-layer composite film is cut into film sheets of predetermined size, with a length of 50-70cm and a width of 36-50cm, corresponding to the unfolded size of the finished bag. During the bag making process, the hemp fiber reinforcement mesh is first pre-laid on the bottom of the bag body corresponding to the position of the inner layer film. It is then embedded into the inner layer under a pressure of 0.3-0.5MPa by a roller pressing device. Then, it is heat-sealed for 3-5 seconds at 160℃ and 0.5MPa pressure, which at the same time forms a bottom seal and a cross-shaped reinforcing rib. The rib width is 3-5mm and the thickness is 150-200μm.

[0085] S4. Functional Structure Processing:

[0086] S4a. Apply a 1-3 wt% carboxymethylated cellulose nanocrystal dispersion to the bottom of the inner wall of the bag, 0.5-2.0 cm above the heat-sealing line. Dry in a 0.5-2T magnetic field at 40-50℃ for 30-60 minutes to form a vertically oriented cellulose nanocrystal array with an array density of 102. 6 -10 7 Roots / mm², covering an area of ​​20-40% of the total bottom area of ​​the inner wall;

[0087] S4b. A micro-conical groove water storage area is processed on the inner wall area at the top of the bag using laser micro-engraving technology, with a groove depth of 100-300μm;

[0088] S4c. Carboxymethylated cellulose long fibers with a diameter of 20-50μm are used as hydrophilic and water-conducting fibers, with their two ends fixed in the cellulose nanocrystal array region and the water storage area groove, respectively; fixed by bio-adhesive or hot pressing to avoid falling off in actual use.

[0089] S4d. Deposit a polydopamine photothermal layer on the surface of the groove in the water storage area, and immerse it in dopamine hydrochloride Tris-HCl buffer for 24-48 hours at pH=8.5 to form a photothermal layer with a thickness of 50-100nm.

[0090] S5. Preparation of the indicator window: Apply pH indicator window gel to a predetermined position on the outer wall of the bag. The gel composition by mass percentage is: 0.5-1.5% bromocresol purple, 2-4% silica fluorescent microspheres, and 94.5-97.5% hydroxyethyl cellulose gel. The coating thickness is 20-50 μm, and it is dried and cured at 40℃. The pH response threshold of the indicator window is 6.0-6.5±0.2.

[0091] S6. Post-processing and packaging: The finished bags are subjected to ultraviolet sterilization treatment, and the sealing performance, pH indicator window function and photothermal layer performance are tested. Qualified products are packaged and put into storage. Specific Implementation Example 1:

[0093] A food storage bag for balanced preservation includes a three-layer composite film bag body. The inner layer comprises the following raw materials in parts by weight: 70 parts polylactic acid, 28 parts polybutylene adipate terephthalate, 2 parts modified hemp fiber, 1.5 parts composite antibacterial agent, and 0.5 parts ADR chain extender. The outer layer of the three-layer composite film bag body comprises the following raw materials in parts by weight: 80 parts polylactic acid and 20 parts polybutylene adipate terephthalate. The middle support layer of the three-layer composite film bag body comprises the following raw materials in parts by weight: 70 parts high-density polyethylene, 15 parts metallocene polyethylene, 8 parts polyethylene grafted maleic anhydride, 7 parts TPE, 5 parts nano zinc oxide, and 1.0 part coupling agent. The pH indicator window contains the following components in weight percentage: 1.0% bromocresol purple, 3% silica fluorescent microspheres, and 96% hydroxyethyl cellulose gel.

[0094] Weigh out polylactic acid, polybutylene adipate terephthalate, modified hemp fiber, titanium dioxide and graphene oxide composite antibacterial agent, and ADR chain extender according to weight parts, and mix them in a high-speed mixer at 60-70℃ for 5-10 minutes. Discharge and set aside. Weigh out polylactic acid and PBAT according to weight parts, and mix them in a high-speed mixer at 55-65℃ for 5-8 minutes. Discharge and set aside. Weigh out high-density polyethylene and metallocene polyethylene according to weight parts, add nano zinc oxide and coupling agent, and mix at 80-90℃ for 8-12 minutes to fully surface treat the nano zinc oxide. Then add polyethylene grafted with maleic anhydride and TPE, and continue mixing at 75-85℃ for 5-8 minutes. Discharge and set aside.

[0095] The inner layer extruder temperature is set to 170℃; the middle layer extruder temperature is set to 190℃; and the outer layer extruder temperature is set to 160℃. The three-layer melt is composite blow-molded through a co-extrusion die, with the blow-up ratio controlled at 3.0 and the cooling air ring temperature at 10-15℃, to obtain a three-layer composite film preform. By adjusting the screw speed of the three-layer extruder, the thickness ratio of the inner, middle, and outer layers is controlled to be 1:2.0:1, with a total film thickness of 50-70μm. The three-layer composite film is then cut into predetermined sizes. The membrane has a length of 50-70cm and a width of 36-50cm, corresponding to the unfolded size of the finished bag. During the bag making process, the hemp fiber reinforcing mesh is first pre-laid on the bottom of the bag body corresponding to the inner layer membrane position. It is then embedded into the inner layer by a roller pressing device under a pressure of 0.3-0.5MPa. Then, it is heat-sealed at 160℃ and 0.5MPa pressure for 3-5 seconds, which simultaneously forms a bottom seal and cross-shaped reinforcing ribs. The rib width is 3-5mm and the thickness is 150-200μm.

[0096] A 2wt% carboxymethylated cellulose nanocrystal dispersion was coated onto the bottom of the inner wall of the bag, 0.5-2.0 cm above the heat-sealing line. This was then dried at 45°C under a 1T magnetic field for 45 minutes to form a vertically oriented cellulose nanocrystal array with an array density of 6 × 10⁻⁶. 6 root / mm 2 The coverage area accounts for 20-40% of the total area of ​​the bottom of the inner wall; a micro-conical groove water storage area is processed in the inner wall area at the top of the bag using laser micro-engraving technology, with a groove depth of 100-300μm; long carboxymethyl cellulose fibers with a diameter of 20-50μm are used as hydrophilic water-conducting fibers, with their two ends fixed in the cellulose nanocrystal array area and the water storage area groove, respectively; a polydopamine photothermal layer is deposited on the surface of the water storage area groove, and then immersed in dopamine hydrochloride Tris-HCl buffer for 36 hours at pH=8.5 to form a photothermal layer with a thickness of 50-100nm; indicator window fabrication: pH indicator window gel is coated at a predetermined position on the outer wall of the bag, with the gel composition by mass percentage as follows: bromocresol purple 0.5-1.5%, silica fluorescent microspheres 2-4%, hydroxyethyl cellulose gel 94.5-97.5%, coating thickness 20-50μm, and dried and cured at 40℃; the indicator window response threshold pH is 6.3. Specific Implementation Example 2:

[0098] A food storage bag, primarily used for aquatic product preservation, comprises a three-layer composite film bag body. The inner layer comprises the following raw materials in parts by weight: 65 parts polylactic acid, 32 parts polybutylene adipate terephthalate, 1.5 parts modified hemp fiber, 2.0 parts composite antibacterial agent, and 0.7 parts ADR chain extender. The outer layer of the three-layer composite film bag body comprises the following raw materials in parts by weight: 85 parts polylactic acid and 15 parts polybutylene adipate terephthalate. The intermediate support layer of the three-layer composite film bag body comprises the following raw materials in parts by weight: 75 parts high-density polyethylene, 12 parts metallocene polyethylene, 6 parts polyethylene grafted maleic anhydride, 7 parts SEBS, 6 parts nano zinc oxide, and 1.2 parts coupling agent. The pH indicator window contains the following components in weight percentage: 1.0% bromocresol purple, 3% silica fluorescent microspheres, and 96% hydroxyethyl cellulose gel.

[0099] Weigh out polylactic acid, polybutylene adipate terephthalate, modified hemp fiber, titanium dioxide and graphene oxide composite antibacterial agent, and ADR chain extender according to weight parts, and mix them in a high-speed mixer at 68°C for 10 minutes. Discharge and set aside. Weigh out polylactic acid and PBAT according to weight parts, and mix them in a high-speed mixer at 55-65°C for 5-8 minutes. Discharge and set aside. Weigh out high-density polyethylene and metallocene polyethylene according to weight parts, add nano zinc oxide and coupling agent, and mix at 80-90°C for 8-12 minutes to fully surface treat the nano zinc oxide. Then add polyethylene grafted with maleic anhydride and TPE, and continue mixing at 75-85°C for 5-8 minutes. Discharge and set aside.

[0100] The inner layer extruder temperature is set to 175℃; the middle layer extruder temperature is set to 195℃; and the outer layer extruder temperature is set to 165℃. The three-layer melt is composite blow-molded through a co-extrusion die, with the blow-up ratio controlled at 3.2 and the cooling air ring temperature at 10-15℃, to obtain a three-layer composite film preform. By adjusting the screw speed of the three-layer extruder, the thickness ratio of the inner, middle, and outer layers is controlled to be 1:1.8:1, with a total film thickness of 50-70μm. The three-layer composite film is then cut into predetermined sizes. The membrane has a length of 50-70cm and a width of 36-50cm, corresponding to the unfolded size of the finished bag. During the bag making process, the hemp fiber reinforcing mesh is first pre-laid on the bottom of the bag body corresponding to the inner layer membrane position. It is then embedded into the inner layer by a roller pressing device under a pressure of 0.3-0.5MPa. Then, it is heat-sealed at 160℃ and 0.5MPa pressure for 3-5 seconds, which simultaneously forms a bottom seal and cross-shaped reinforcing ribs. The rib width is 3-5mm and the thickness is 150-200μm.

[0101] A 2.5wt% carboxymethylated cellulose nanocrystal dispersion was coated on the bottom of the inner wall of the bag, 0.5-2.0 cm above the heat-sealing line. This was then dried at 48°C for 40 minutes under a 1.5T magnetic field to form a vertically oriented cellulose nanocrystal array with an array density of 8 × 10⁻⁶. 6 root / mm2 The coverage area accounts for 20-40% of the total area of ​​the bottom of the inner wall; a micro-conical groove water storage area is processed in the inner wall area at the top of the bag using laser micro-engraving technology, with a groove depth of 100-300μm; long carboxymethyl cellulose fibers with a diameter of 20-50μm are used as hydrophilic water-conducting fibers, with their two ends fixed in the cellulose nanocrystal array area and the water storage area groove, respectively; a polydopamine photothermal layer is deposited on the surface of the water storage area groove, and then immersed in dopamine hydrochloride Tris-HCl buffer for 40 hours at pH=8.5 to form a photothermal layer with a thickness of 50-100nm; indicator window fabrication: pH indicator window gel is coated at a predetermined position on the outer wall of the bag, with the gel composition by mass percentage as follows: bromocresol purple 0.5-1.5%, silica fluorescent microspheres 2-4%, hydroxyethyl cellulose gel 94.5-97.5%, coating thickness 20-50μm, and dried and cured at 40℃; due to the increase in pH value when fish spoil, the pH response threshold of the indicator window is 6.5. Specific Implementation Example 3:

[0103] A food storage bag, primarily used for preserving fruits and vegetables, comprises a three-layer composite film bag body. The inner layer comprises the following raw materials in parts by weight: 80 parts polylactic acid, 20 parts polybutylene adipate terephthalate, 1.0 part modified hemp fiber, 0.5 parts composite antibacterial agent, and 0.3 parts ADR chain extender. The outer layer of the three-layer composite film bag body comprises the following raw materials in parts by weight: 90 parts polylactic acid and 10 parts polybutylene adipate terephthalate. The intermediate support layer of the three-layer composite film bag body comprises the following raw materials in parts by weight: 65 parts high-density polyethylene, 18 parts metallocene polyethylene, 7 parts polyethylene grafted with maleic anhydride, 8 parts TPE, 4 parts nano zinc oxide, and 0.8 parts coupling agent. The pH indicator window contains the following components in weight percentage: 1.0% bromocresol purple, 3% silica fluorescent microspheres, and 96% hydroxyethyl cellulose gel.

[0104] Weigh out polylactic acid, polybutylene adipate terephthalate, modified hemp fiber, titanium dioxide and graphene oxide composite antibacterial agent, and ADR chain extender according to weight parts, and mix them in a high-speed mixer at 62°C for 6 minutes. Discharge and set aside. Weigh out polylactic acid and PBAT according to weight parts, and mix them in a high-speed mixer at 55-65°C for 5-8 minutes. Discharge and set aside. Weigh out high-density polyethylene and metallocene polyethylene according to weight parts, add nano zinc oxide and coupling agent, and mix at 80-90°C for 8-12 minutes to fully surface treat the nano zinc oxide. Then add polyethylene grafted with maleic anhydride and TPE, and continue mixing at 75-85°C for 5-8 minutes. Discharge and set aside.

[0105] The inner layer extruder temperature is set to 165℃; the middle layer extruder temperature is set to 185℃; and the outer layer extruder temperature is set to 155℃. The three-layer melt is composite blow-molded through a co-extrusion die, with the blow-up ratio controlled at 2.8 and the cooling air ring temperature at 10-15℃, to obtain a three-layer composite film preform. By adjusting the screw speed of the three-layer extruder, the thickness ratio of the inner, middle, and outer layers is controlled to be 1:2.2:1, with a total film thickness of 50-70μm. The three-layer composite film is then cut into predetermined sizes. The membrane has a length of 50-70cm and a width of 36-50cm, corresponding to the unfolded size of the finished bag. During the bag making process, the hemp fiber reinforcing mesh is first pre-laid on the bottom of the bag body corresponding to the inner layer membrane position. It is then embedded into the inner layer by a roller pressing device under a pressure of 0.3-0.5MPa. Then, it is heat-sealed at 160℃ and 0.5MPa pressure for 3-5 seconds, which simultaneously forms a bottom seal and cross-shaped reinforcing ribs. The rib width is 3-5mm and the thickness is 150-200μm.

[0106] A 1.5 wt% carboxymethylated cellulose nanocrystal dispersion was coated onto the bottom of the inner wall of the bag, 0.5-2.0 cm above the heat-sealing line. This was then dried at 42°C under a 0.8 T magnetic field for 50 minutes to form a vertically oriented cellulose nanocrystal array with an array density of 4 × 10⁻⁶. 6 root / mm 2 The coverage area accounts for 20-40% of the total area of ​​the bottom of the inner wall; a micro-conical groove water storage area is processed in the inner wall area at the top of the bag using laser micro-engraving technology, with a groove depth of 150μm; long carboxymethyl cellulose fibers with a diameter of 20-50μm are used as hydrophilic water-conducting fibers, with their two ends fixed in the cellulose nanocrystal array area and the water storage groove, respectively; a polydopamine photothermal layer is deposited on the surface of the water storage groove, and then immersed in dopamine hydrochloride Tris-HCl buffer for 28 hours at pH=8.5 to form a photothermal layer with a thickness of 50-100nm; indicator window fabrication: pH indicator window gel is coated at a predetermined position on the outer wall of the bag, with the gel composition by mass percentage as follows: bromocresol purple 0.5-1.5%, silica fluorescent microspheres 2-4%, hydroxyethyl cellulose gel 94.5-97.5%, coating thickness 20-50μm, and dried and cured at 40℃; for fruit and vegetable spoilage, the pH decrease is more obvious, and the indicator window response threshold pH is 6.0.

[0107] The samples from Specific Example 1, Specific Example 2 and Specific Example 3 were used for salmon and strawberry preservation, and their 24-hour antibacterial rate, water conduction rate, cost, shelf life and weight loss rate were tested.

[0108] Table 1 Performance Comparison Table

[0109]

[0110] Comparative Example 1:

[0111] PE food storage bags with a thickness of 50μm are used.

[0112] Comparative Example 2:

[0113] Except for the inner layer not containing a composite antibacterial agent, the rest is the same as in Specific Example 1.

[0114] Comparative Example 3:

[0115] The cellulose nanocrystal array, hydrophilic water-conducting fiber, and water storage area are not included; the rest is the same as in Specific Example 1.

[0116] Comparative Example 4:

[0117] A single-layer membrane (50 μm thick) was prepared using a specific inner layer formulation from one embodiment, without an outer layer or pH indicator window.

[0118] Conduct material property testing:

[0119] Degradation performance: The samples were placed in a composting environment at 30℃ and 60% humidity, weighed weekly, and the degradation rate was calculated after 60 days.

[0120] Mechanical properties: Tensile strength and elongation at break were tested according to GB / T 1040.3-2006.

[0121] Transmittance: The transmittance at wavelengths of 400-800 nm was measured using a UV-Vis spectrophotometer.

[0122] Preservation effect test: Strawberries (200g / bag) and pork (200g / bag) were selected as test subjects and placed in an environment of 25℃. The mold growth of the samples was observed daily, and the pH value and total bacterial count in the bags were tested (GB 4789.2-2016). The weight loss rate of strawberries (weight change / initial weight) and the time of spoilage of pork (time when off-odor appeared) were recorded.

[0123] Manually adjust the pH value inside the bag (4.0~7.0), observe the response time of the color change of the pH indicator window, and record the correspondence between the color change and the actual pH value.

[0124] Structural stability test: A 500g weight was placed inside the bag to simulate daily use pressure. The damage to the bottom reinforcing ribs and fiber reinforcement mesh was observed. After folding the bag 100 times, the sealing performance of the bag was tested (air bubbles were observed when it was squeezed underwater).

[0125] Table 2 Material property results

[0126]

[0127] The results above show that the degradation rate of Example 1 was significantly higher than that of Comparative Example 1 (PE material), indicating that the PLA / PBAT composite substrate can effectively solve the white pollution problem. The degradation rates of Comparative Examples 2, 3, and 4 were close to those of Example 1, indicating that the antibacterial agent, moisture management structure, and double-layer design had little impact on degradation performance. Regarding mechanical properties, Example 1 had better tensile strength than Comparative Examples 1 and 3, but slightly lower elongation at break, indicating that the double-layer structure and hemp fiber reinforcement improved material rigidity, meeting daily usage requirements.

[0128] Regarding antibacterial effects, the mold growth time of strawberries and the spoilage time of pork in the first specific example group were both longer than those in the second comparative example group, proving that the compound antibacterial agent can inhibit microbial reproduction and extend shelf life. In terms of moisture management, the weight loss rate of strawberries in the first specific example group was significantly lower than that in the third comparative example group. This is because the cellulose nanocrystal array guides condensate to the water storage area through hydrophilic fibers, reducing local humidity, and the polydopamine photothermal layer can utilize light energy to evaporate moisture, maintaining a dry environment inside the bag.

[0129] In a specific embodiment, the pH indicator window turns red within 10 seconds when the pH is ≤ 6.3, consistent with the pattern of pH decrease caused by acidic substances produced during food spoilage. This provides a direct warning of food safety risks and addresses the limitation of traditional food storage bags in monitoring pH levels. The cross-shaped reinforcing ribs and hemp fiber reinforcement mesh result in a low bottom breakage rate for the first embodiment, and no loss of sealing after folding, superior to other groups, demonstrating that the structural design improves durability.

[0130] The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which this invention pertains may make various modifications or additions to the described specific embodiments or use similar methods to substitute them, without departing from the spirit of the invention or exceeding the scope defined by the appended claims.

Claims

1. A food preservation bag for food storage, characterized in that, include: Three-layer composite film bag; The inner layer of the three-layer composite film bag comprises the following raw materials in parts by weight: 60-80 parts of polylactic acid, 20-40 parts of polybutylene adipate terephthalate, 1-3 parts of modified hemp fiber, 0.5-2 parts of composite antibacterial agent, and 0.3-0.8 parts of ADR chain extender; The outer layer of the three-layer composite film bag comprises the following raw materials in parts by weight: 70-90 parts of polylactic acid and 10-30 parts of polybutylene terephthalate. The intermediate support layer of the three-layer composite membrane bag comprises the following raw materials in parts by weight: 60-80 parts of high-density polyethylene, 10-20 parts of metallocene polyethylene, 5-10 parts of polyethylene grafted with maleic anhydride, 5-10 parts of TPE or SEBS, 3-8 parts of nano zinc oxide, and 0.5-1.5 parts of coupling agent. The total thickness of the three-layer composite membrane bag is 50~70μm, and the thickness ratio of the inner layer, the middle support layer and the outer layer is 1:1.5~2.5:

1. The bottom of the inner wall of the inner layer of the three-layer composite membrane bag is provided with a cellulose nanocrystal array, the cellulose nanocrystal array covering an area of ​​20-40% of the total area of ​​the bottom of the inner wall. The top inner wall of the bag is provided with a laser-engraved micro-conical groove water storage area. Hydrophilic water-conducting fibers connect the cellulose nanocrystal array and the water storage area. The surface of the water storage area is covered with a polydopamine photothermal layer with a thickness of 50-100nm. The outer wall of the three-layer composite membrane bag is provided with a pH indicator window, which contains the following components by mass percentage: bromocresol purple 0.5~1.5%, silica fluorescent microspheres 2~4%, and hydroxyethyl cellulose gel 94.5~97.5%; The pH indicator window changes color when the pH exceeds a threshold range.

2. A food storage bag as described in claim 1, characterized in that, The modified hemp fiber is treated with silane coupling agent KH-550 and has a length of 50~200μm and a diameter of 10~30μm. The composite antibacterial agent is a titanium dioxide and graphene oxide antibacterial agent, with a mass ratio of titanium dioxide to graphene oxide of 1:0.2~0.

5.

3. A food storage bag as described in claim 1, characterized in that, The cellulose nanocrystal array is located 0.5-2.0 cm above the heat-sealing line at the bottom of the bag. It is composed of carboxymethylated cellulose nanocrystals with a diameter of 20-50 nm, oriented and assembled using a 0.5-2T magnetic field, with an array density of 102. 6 ~10 7 root / mm 2 ; The hydrophilic and water-conducting fiber is a long carboxymethylated cellulose fiber with a diameter of 20~50μm.

4. A food storage bag as described in claim 1, characterized in that, The depth of the micro-conical groove water storage area is 100~300μm; The visible light absorption rate of the polydopamine photothermal layer is ≥90%.

5. A food storage bag as described in claim 1, characterized in that, The dimensions of the bag are 25-35cm in length, 18-25cm in width, and 10-25cm in height; Among them, the bottom of the bag is heat-sealed to form a cross-shaped reinforcing rib, with a rib width of 3~5mm and a thickness of 150~200μm; The bottom of the inner layer of the bag is embedded with hemp fiber reinforcement mesh with a density of 20-30 fibers / cm².

6. A method for preparing a food storage bag as described in any one of claims 1-5, characterized in that, Includes the following steps: S1. Material preparation and pretreatment: S1a. Preparation of inner layer materials: Weigh polylactic acid, polybutylene adipate terephthalate, modified hemp fiber, titanium dioxide and graphene oxide composite antibacterial agent, and ADR chain extender according to the weight parts, place them in a high-speed mixer and mix at 60-70℃ for 5-10 minutes, and discharge for later use; S1b. Preparation of outer layer material: Weigh polylactic acid and PBAT according to the weight parts, place them in a high-speed mixer and mix at 55-65℃ for 5-8 minutes, then discharge for later use; S1c. Preparation of intermediate layer material: Weigh high-density polyethylene and metallocene polyethylene according to the weight parts, add nano zinc oxide and coupling agent, mix at 80-90℃ for 8-12 minutes to fully surface treat the nano zinc oxide; then add polyethylene grafted with maleic anhydride and TPE, continue mixing at 75-85℃ for 5-8 minutes, and discharge for later use. S2, Three-layer co-extrusion blown film: Three single-screw extruders are used to separately feed the inner layer, outer layer, and middle layer materials, wherein: The inner extruder temperature is set to 160-180℃; The temperature of the intermediate layer extruder is set to 180-200℃; The outer extruder temperature is set to 150-170℃; The three-layer melt is composite blow-molded through a co-extrusion die, with the blow-up ratio controlled at 2.5-3.5 and the cooling air ring temperature at 10-15℃, to obtain a three-layer composite preform. By adjusting the screw speed of the three-layer extruder, the thickness ratio of the inner layer, middle layer, and outer layer can be controlled to be 1:1.5-2.5:1, with a total film thickness of 50-70μm; S3. Bag making and reinforcement: The three-layer composite film is cut into film sheets of predetermined size, with a length of 50-70cm and a width of 36-50cm, corresponding to the unfolded size of the finished bag. During the bag making process, the hemp fiber reinforcement mesh is first pre-laid on the bottom of the bag body corresponding to the inner layer film position. It is then embedded into the inner layer by a roller pressing device under a pressure of 0.3-0.5MPa. Then, it is heat-sealed at 160℃ and 0.5MPa pressure for 3-5 seconds, which simultaneously forms a bottom seal and cross-shaped reinforcing ribs. The rib width is 3-5mm and the thickness is 150-200μm. S4. Functional Structure Processing: S4a. Apply a 1-3wt% carboxymethylated cellulose nanocrystal dispersion to the bottom of the inner wall of the bag, 0.5-2.0cm above the heat-sealing line, and dry it at 40-50℃ in a 0.5-2T magnetic field for 30-60 minutes to form a vertically oriented cellulose nanocrystal array with an array density of 106-107 nanocrystals / mm², covering an area of ​​20-40% of the total area of ​​the bottom of the inner wall. S4b. A micro-conical groove water storage area is processed on the inner wall area at the top of the bag using laser micro-engraving technology, with a groove depth of 100-300μm; S4c. Carboxymethylated cellulose long fibers with a diameter of 20-50 μm are used as hydrophilic water-conducting fibers, with their two ends fixed in the cellulose nanocrystal array region and the water storage region groove, respectively. S4d. Deposit a polydopamine photothermal layer on the surface of the groove in the water storage area, and immerse it in dopamine hydrochloride Tris-HCl buffer for 24-48 hours at pH=8.5 to form a photothermal layer with a thickness of 50-100nm. S5. Preparation of the indicator window: Apply pH indicator window gel to a predetermined position on the outer wall of the bag. The gel composition by mass percentage is: 0.5-1.5% bromocresol purple, 2-4% silica fluorescent microspheres, and 94.5-97.5% hydroxyethyl cellulose gel. The coating thickness is 20-50 μm, and it is dried and cured at 40℃. The pH response threshold of the indicator window is 6.0-6.5±0.

2. S6. Post-processing and packaging: The finished bags are subjected to ultraviolet sterilization treatment, and the sealing performance, pH indicator window function and photothermal layer performance are tested. Qualified products are packaged and put into storage.

7. A method for preparing a food storage bag as described in claim 6, characterized in that, In step S2, the melt flow rate ratio of the three-layer extruder is controlled to be inner layer: middle layer: outer layer = 1:1.8-2.2:1.

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